Catalytic conversion of hydrocarbon oils



United States Patent O 2,703,308 cAT-ALYTIC CoNvRtsjrogtoFHYDliocTAiiBoN IL Alex. G. ob'ld, Springlieldf, and'Heingz Heinemann,:Drexel Hill, Pa., as'signors to Houdr'y Process Corporation,

The present inventioni relates `to i catalytic conversion ofhydrocarbons` above' the4 gasoline boil-ing range', such as topped'crude` oils, to high yields 'of gasoline of -g'ood-antiknock quality.The invention is particularly concerned w1th catalytic cracking of such?hydrocarbonsathigh` pressure in the presence of excess hydrogen an'dthe' processing of selected portions of 'the cracked effluent `toeffectl conversion of substantially the entire initial' charge to" highyields of gasoline of good octane rating.

vAmong the objectsI of the inventionis'r to provide an efficient processfor the 'conversion of higher boiling oils to quantities of high qualitygasoline alriio'st equal to or exceeding 100% by volume of the charge.

niponerit intimatelyminor am'onntf of? component geriat'ing activity.The'crackedi vp r Y' sensed and: fr @donated to p ovide a High.r @etaitlight gasoline fractionated ampli relatively peer O'Ctneqlity includinglarge Ofltsb-lirig the gasolinera g'eg while e residu ottoms a'e recy dto the hydrogenative ng zon all ot the ifiig thus ultimately' cracked toga'soliiieaiid lighter" ydrocar- Beust peer "pinna fraction w ki will`be rich in Iipltl'the'riesL lbl toarontic's, is upgraded invention. Theoperation of the invention willbemnder;

stood from the' description which- -follows readirifconnection with the'accompanying flow chart illustrating a-p'retened-processing operation. y

The topped crude charge (.11) which may contain the entire' bottoms',Ipreferably after removal of at least part of tl'ie mineral` saltcontent, is heated tof're'actiontemperature and together 'with addedhydrogen or11 hydrogen' rich gas (2) in required proportions' i's`continuously charged at controlled fates to the hydrogenative crackingzone (3), Whichf is maintained under required conditions oftempera'tureA and pressure. The cracked product is frac-tionated"(,4)'to separate the same (ini order of increasing boilirlg range) intohydrogen (5'), light normallygaseous'hyydrocarbons2 in the C11-C3` range(6),l a Q4` fraction (.7), a high octane Cs-Cs out (8) a naphtha :cut-`including Vhigher boilingy components of the gasoline range (9.) and`residual bottoms a rlhe residual bottoms fraction from the`hydrogenative ycracking is recycled to the hydrogenative cracking zone(3,)Y as Well as theV excess hydrogen (5).l Themaphtha -cut (9) ispassed to a dehydrogenation zone (11) where it-iis upgradedpriucipallyby conversionof naphthenesn to 'aromatics in the presence of adehydrogenationcatalyst, '-the effluent therefrom being distilled (12)toproduce a re"- 2,703,308 Patented Mar. 1, 1955 ICC formed naphthafraction (13); and the residue from' this distillation, above desiredgasoline boiling range, is re'- cycled (14) to the hydrogenativecracking step. Hydrogen produced in the dehydrogenation is rceovered(15) and the hydrogen rich gas returnedk for use 'in the hydrogenativecracking step'. The reformed naphtha (13) is blended with the previoushighy octane Cs/-Cs cut from (8), and the blend adjusted and stabilizedby addition of a suitable quantity ofthe C4 product from (7 as indicatedat (.16), to furnish gasoline of desired vapor pres'- sure.

AsI indicated, the hydrogen produced in the dehydrogenation step (.11)is advantageously recycled to the cracking step which uses up hydrogen.Additional hydrogen is available from colsingv of the xed gas from (6)so that by employing the latter step' the processcan be made almost orentirely self-sufficient in hydrogen requirements. Cokingrmay bee'ife'cted, as indicated at (17) by thermal or catalytic decorrxpositionof the fixed gas. The present invention is not limited to any particularmethod of cokin'g of the fixed'y gas and various means will be apparentto those skilled in the art. For instance, the gas rn'ay 'be convertedby reaction with steam to CO or CO2'4 plus hydrogen' as in the knownwater-gas processes, inthe presence of nickel oxide or other suitablecatalyst, 'andfthe hydrogen-rich gas evolved recovered (118) andrecyc'ied-to the hydrogenative cracking zone.

l* willfbe understoodtthat inpr'actical operation of the describedprocess, suitable provision will be' madein knownmaniier for vheatexchange of products' and charge 'as may be'convenient, aswell as foradjustment of pressure and temper'a'turevr for desired' stripping ofgases, condeiisatiori` of liquid products and repressuringof therecycled fraction.

Although other feedv stocks, 'such as heavy gas` oils or residuurn fromthermal or catalytic cracking may be used ge' for? hydrogenative'cracking in' zone 3*, one of the tant advantages of` the present processlies in the fact that high boiling portions of the crude oils includingthe itars' and bottoms can be eiiiciently handled therein. Rnovalof atleasta portion of the salts .generally contained the crude oil isrecommended particularly with sto'c'ks other't'han-th'oseof naturallylow salt content.

While" such removal is not indispensabley for operation of the presentprocess, the accumulation of suchI salts' or residues therefrom in the'cracking zone in= addition to easing 'corrosion problems, Vmay shortenthe on-strean-l peiiodsfof operationand deactivate thecatalyst to'thecxtent "ofi curtailiilg` the useful life thereof. Desalting may beetfected in known manner, for instance by chemical or electrical methodsor' by heating andt settling,` capable of reducing the salt `content to'preferably less than! Seli) pounds per l000'lbarrel's offoil;-c'entr'ifuging may beffound vadvalit'a'geous. I-f the reduced `crudecharged to' the hydiiog'e'nati've cracking. zone'is one which has had asrifiuch as- 511f0% 'ofthe' bottoms removed by" deaspha'ltizing or tarseparation procedures, the removed portion will conta" lthe preponderantpart ofthe salts and separate desaltijiig "f thereclucede crude insuchfcases ordinarily will ne: lo-Dfiel;

In the hydoge'nafiv cracking Zone, the conditions arpreferablymaintained to favor hydrogenativ'e crackiig of the charge" WithoutVexcessive formation of low molecular weight gases and with littlel orYpractically" no incremental coke production, such that ythe process canbe operated for comparatively' long periods without 11e- 'cesfsitatingperiodicv catalyst' regeneration'. Thesel conditions include pressuresabove 750* pounds per square inch, temperatures of about 800y tol000 F.,and space rates of upto about 6 volumes of oil (as liquid) per hour pervolumey of catalyst, hydrogen being added with the charge at the rate of3 or more r'nols per mol to total hydrocarbon charged'. In the'preferred opera-tion pres'- suresA of 1,500 to 3500 ypounds are employedat temperatures below 900 F. and space rates of about 0.5' up to about4,. hydrogen being added at rates of atleast 5 mols and up to 10-15 molsper inol of total hydrocarbon charged. As catalyst there may be employedcomposited Contact masses composed of a 'component having crackingactivity intimately 4associated with a small portion of a componenthaving hydrogenative' activity. The preferred composited catalysts arethose in which the crack ing component is one of comparatively highcracking activity, such as acid activated montrnorillonite clays, driedsiliceous gels of the silica-alumina and silica-magnesia type, andHF-activated alumina. The hydrogenating component is likewise one ofselective high activity for this function and is preferably an oxide ofnickel or molybdenum, the former in amounts of up to by weight of thecatalyst and the latter generally in smaller amount as up to about 2% byweight of the catalyst.

The operating conditions in the hydrogenative cracking step are selectedand correlated to obtain only moderate conversion severity particularlyif regeneration of the catalyst is not desired to be practiced, and toavoid loss of large amounts of the hydrocarbon charge to the formationof low molecular weight hydrocarbon gases. In general, it is perferredto operate under conditions obtaining about 60% conversion per pass, orstated otherwise at recycle ratios of about l/ 1 to 4/1.

In the above described type of operation the catalytic gas oil isrecycled to extinction, that is until it is converted entirely togasoline of desired end point with the concomitant formation of C4hydrocarbons and lower molecular weight hydrocarbon gases. The choice ofconversion severity will be governed largely by the butane requirementsfor the gasoline produced in the process or needed elsewhere in therenery. With increasing severity there is a corresponding increase information of C4 hydrocarbons accompanied by an increase in the amount oflower molecular weight hydrocarbon gases produced. At lower conversionlevels, of course, there is a smaller amount of C4 hydrocarbons andlower molecular weight gases formed, but likewise the amount of gasolineproduced per pass is also lowered, so that increased recycle ratios arerequired and as a result thereof the amount of fresh feed that can beconverted in a given time in the reactor of fixed capacity iscorrespondingly reduced.

In hydrogenative cracking operations carried out under the conditionsabove described, for most of the usual charge stocks, continuouson-stream periods as long as six months or more are possible. The lengthof the continuous on-stream period will depend almost entirely on thesalt content of the charge and ability of the reactor and the catalystto accumulate this salt without affecting the desired hydrocarbonconversion reactions, since outside of a possible initial deposition ofa negligible quantity of coke at the beginning of the on-stream periodthere is no incremental coke deposition during continuous operation ofthe hydrogenative cracking process. Heavy metals that may be depositedin the catalyst from the charge are not necessarily detrimental and mayeven sclerve to enhance the hydrogenative function of the cata yst.

The following illustrates typical results obtained in a hydrogenativecracking operation carried out for several days on an entire bottomsfraction of East Texas crude oil (40% residuum) of 23.7 API gravity andboiling in the range of 430 F. initial, 50% at 855 F., 80% at 985 F. Theoperating conditions employed were 825 F. at a total pressure of 3500 p.s. i., at a space rate of one volume of oil per hour per volume ofcatalyst. 6 mols of hydrogen being added per mol of total hydrocarboncharged; the catalyst being 2.0% NiO on synthetic silica-alumina gel(87.5 SiOz-l2.5 A1203). For total conversion of the charge to gasolineand lighter hydrocarbons a recycle ratio of 3.8 was employed, with thefollowing ultimate yields:

Gasoline, 385 F. at 90%; vol. percent fresh feed 102. C4 cut, vol.percent fresh feed 16 Dry gas, wt. percent fresh feed 10.1 Coke Nil Theparticular cut point to be employed for the recycled catalytic gas oil(or the end point of the gasoline to be sent to reforming) will dependlargely on the nature of the initial fresh charge and the chemicalcomposition or octane rating of various successive narrow cuts taken inthe S50-450 F. boiling range of the hydrogenatively cracking euent(synthetic crude). In the particular embodiment illustrated in theaccompanying ow chart materials boiling above 370 F. are recycled to thehydrogenative cracking zone 3. In other operations, depending upon thecharge stock and on the desired final products, it may be preferred tocut the gas oil for recycling at a higher or lower point as for instanceat 350 F. or at a point as high as 450 F.

Like considerations apply in thc selection of the initial cut point forthe low octane naphtha fraction sent to reforming (9). This cut, ofcourse, will include all of the hydrocarbons boiling below the recycledgas oil exclusive of the light ends (8). As a general rule reforming ofproducts boiling below about 180 F. need not be practiced, and in someinstances it may be preferred to reform only the products above a highercut point as those boiling above about 220-240" F.

The reforming of the naphtha is carried out under conditions favoringdehydrogenation of naphthenes and is preferably unaccompanied bymaterial cracking of the charge. For use in this step knowndehydrogenation catalysts of the indicated selectivity can be employedsuch as those containing up to 8-15% molybdena on activated alumina, ornickel or nickel oxide on various inert carriers. Catalysts which havesignificant cracking activity, even if in addition to dehydrogenatingactivity, are best avoided in the reforming operation. A preferredcatalyst for use in this step is that disclosed in our copendingapplication Serial No. 198,469, filed November 30, 1950, comprising Pton an inert support, which support has no significant cracking activity,such as 0.1 to 2% Pt on MgO. Operating conditions for reforming bydehydrogenation include temperatures of about 700-l050 F., the preferredoperating temperature lying in the neighborhood of 950 F. From overallconsiderations pressures in the range of 500 to 1500 p. s. i. arefavored since at increased pressures of about 2000 p. s. i. the crackingreaction is promoted with consequent increased gas production, while atlow pressures in the order of about 300 p. s. i. considerable cokeformation takes place. Hydrogen to oil ratios similar to thoseheretofore disclosed for the cracking operation can be used; ratios aslow as 3.0 mols Hz per mol of naphtha have been found satisfactory. Thespace velocity should be adjusted to favor dehydrogenation and to avoidside reactions such as cracking, so that higher space rates aregenerally preferred above about one volume of oil per hour per volume ofcatalyst and up to about 10.0. The process variables can be so selectedto avoid signicant coke formation, enabling practice of anon-regenerative process. Even if it is desired to operate at higherseverity to obtain optimum octane upgrading, long on-stream periods ofseveral days or more are possible between regenerations.

The following results obtained in the dehydrogenation of an East Texasstraight-run naphtha are typical:

Table Nphtha charged cut lfgfagx' ggx 1.27 Pt on 1.27 Pt on CatalystllolgO lllgO Pressure, p. 8.1. g 600 600 600 Temp. F 950 950 950LSV-vorm /vo 2 4 o. 5 Hnoil ratio. 3 5 3 Pertd, hrS- 0-60 0-30 150-1800-240 xe s:

Gasoline (05+) Vol. Percent. 94. 5 94. IS 94. 1 83. 5 C4 Vol. Percent 3.9 1. 6 1. 8 11. 5 Dry as, t Percent (Ci-Cz) 1. 4 2. 7 2. 9 4. 2 Coke,Wt. Percent 0. 2 0. 02 0. 02 1. 1 Oetanes (CH-gasoline):

CFR-R Clear 72. 4 69. 4 71. 5 82. 8 +3 cc. TEL 87. 5 85. 6 87. 8 93. 7

Since the reforming operation carried out at 11 involves essentiallydehydrogenation of naphthenes there will be an overall net production ofhydrogen, which as indicated in the accompanying flow chart may berecycled to the hydrogen deficient hydrogenative cracking step.

The described process involving hydrogenative cracking withdehydrogenative reforming of a selected naphtha cut therefrom andrecycling of the higher boiling catalytic gas oil, permits conversion oftopped crude oils or of other feed stocks including catalytically orthermally cracked recycle stocks to -110 vol. per cent gasoline ofdesired high octane quality and good lead susceptibility, producingcomparatively small amounts of excess C4s and dry gas, usually inamounts of less than 10-15% by weight of the charge.

In the reforming operation a relatively small amount of products boilingabove the endy pointI of the desired reformed gasoline may belforme'd'.Such higher` 4boiling products can be recycled to hydrogenative crackingas indicated at 14". v

The following eXa'mpleillustrates a combined crackingreformingoperationI in accordance with the invention.

East Texas gas oil is charged' comprising a crude distillate from whichupto 56% of lighterjen'ds and 23% of bottoms were removed, said gas oilhaving an API gravity of 28.9, and boiling in the range of 539 F. to 928F. at 95%. This charge is` lyd'rogenatively cracked over a catalystcomprisingy 2%V nickel on calcined silicaalumina gel (87.5 SiO2-12.5A1203), under conditions includin'g' a pressure of' 3500 p'. s. i. a'nda temperature' of 825 F.,- oil being fed at the' rate of one volume perhour per volume of catalyst, and 4.7' mols of hydrogen being added tothe charge (ba'sed' on total? hydrocarbons). Operating at a recycle'ratio of 1.4/1, the following yields were obtained in a 44' hourperd:

The gasoline from the above operation was fractionated to provide alight fraction and heavier naphtha fraction as follows:

(45 Fraction I (70-230 Octane No.:

CFR-M Clear 82 CFR-R-l-B cc. TEL 93 (55%) Fraction Il (230-375 F.)(containing 31% naphthenes), Octane No.: CFR-M Clear 51 Fraction IIabove was subjected to dehydrogenation over a catalyst comprising 1.2%Pt on precipitated MgO at a temperature of 950 F. and a pressure of 600p. s. i., operating at a space velocity of 2 volumes of oil per hour pervolume of catalyst, with the addition of 3 mols of hydrogen per mol ofcharge. The yields obtained are given below:

Yields:

C11-free gasoline, vol. per cent 89. CFR-M Clear 67.8. CFR-R Clear 78.5.CFR-R (+3 cc. TEL) 94. C4, vol. per cent 6.7. Dry gas, wt. per cent 3.0.H2, produced 1100 cu. ft./bbl.

naphtha.

'Ihe reformed fraction II is recombined with the light gasoline fractionI from above and the hydrogen is recycled, enough of the C4s producedbeing added to bring the gasoline to 10 pound RVP.

The overall balance for the combined operation is as follows:

Gasoline (Cs|-), vol. per cent 94.5 CFR-R (+3 cc. TEL) 93.5 C4, vol. percent 21.5 Dry gas, wt. per cent 9.3

The addition of 5-8% of the C4 fraction to the above gasoline to bringthe same to l0 pounds RVP, will raise the octane numbers of thestabilized gasoline at least about a point.

Obviously many modifications and variations of the invention ashereinbefore set forth may be made without departing from the spirit andscope thereof, and therefore only such limitations should be imposed asare indicated in the appended claims.

We claim as our invention:

1. The method of producing high yields of gasoline of good octanequality which comprises removing from petroleum at least those materialsboiling in the range of gasoline to provide an initial hydrocarboncharge, hydrogenatively cracking said initial hydrocarbon charge 't a"pressure in excess1 of abo't 750vv pounds'lp'er square inch and in thepresence of a catalyst composed of a minor quantity of a componenthaving` selective hydrogenatin'g activity intimately associated with acomponent having cracking activity, removing a hydrogen-rich gas streamfrom the effluent, separating the remainder of the eiiluent intofractions comprising at least: a C-4 fraction, a light gasoline fractionof comparatively high octane value composed of hydrocarbons boilingabovey the C4 fraction and below 240'` F., a cracked naphtha fractionincluding naphthenic hydrocarbons boiling yin: the upper portionl of thegasoline range, and' a residualA gas oil: fraction boiling in a rangeabove saidlasrt namednaphtha fraction; continuously and' exhaustivelyrecyclin'gsaidresidual gas oil fraction to` said hydrogenative cracking,reforming only said cracked naphtha fraction substantially free fromlower boiling hydrocarbons under dehydrogenating conditions and inv thepresence of a dehydrogenating catalyst, said conditions and catalystbeing selected todisfavor substantial coking and cracking of saidnaphtha fraction including' pressure above. 300 pounds per square inch,recovering from products of dehydrogenation a hydrogenrich gas and a'4reformed gasoline fraction of desired end point, returning at least aportion of'` said hydrogen-rich gas from dehydrogenation to saidhydrogenative cracking step, blending said reformed gasoline fractionwith said light gasoline fraction derived from hydrogenative crackingand adding tolthe` blend a sufficient portion of said C-4 fraction' tofproduce gasoline of desired vapor pressure, and recycling tohydrogenative cracking any hydrocarbons boiling above the desired endpoint of the reformed gasoline, whereby all of the hydrocarbons in saidinitial charge are converted to products boiling no higher than saiddesired gasoline end point.

2. The method according to claim 1 wherein said hydrogenative crackingof the initial charge is carried out at temperatures in the range ofabout 800-l000 F. and at pressures of at least 1500 pounds per squareinch.

3. The method according to claim 2 wherein the catalyst employed in thehydrogenative cracking step consists of a silicious cracking componentcontaining nickel as hydrogenating component.

4. The method according to claim l wherein the reforming of said crackednaphtha fraction is effected at temperatures in the range of 700- 0 F.,under pressure of 500 to 15 00 pounds per square inch.

5. The method according to claim 1 wherein said eiiluent fromhydrogenative cracking is separated into fractions including a normallygaseous hydrocarbon fraction.

6. The method according to claim 5 wherein said normally gaseoushydrocarbon fraction is converted to products including hydrogen andsaid hydrogen is recovered for use in said hydrogenative cracking.

7. The method according to claim l wherein said light gasoline fractionseparated from the effluent from hydrogenative cracking has an end pointof about ISO-240 F. and said cracked naphtha fraction boils in a rangethereabove and up to S50-450 F.

8. The method according to claim 1 wherein operating conditions aremaintained during said hydrogenative cracking to effect 20-60%conversion of said initial charge.

9. The method according to claim 8 wherein said operating conditionsinclude temperatures below 900 F., pressure of 1500-3500 pounds persquare inch, liquid space velocity of about 0.5 to about 4 volumes ofhydrocabon charge per hour per volume of catalyst, at least 5 mols ofhydrogen being added per mol of total hydrocarbons charged.

10. The method according to claim 1 wherein said cracked naphthafraction is reformed in the presence of a catalyst comprising platinumon an inert carrier having no substantial cracking activity and at atemperature of about 950 F., said cracked naphtha being charged at aliquid space rate above about l volume of naphtha per hour per volume ofthe catalyst.

l1. The method of producing high yields of gasoline of good octanequality and high lead susceptibility which -comprises feeding a reducedpetroleum crude of essentially above gasoline boiling range to ahydrogenative cracking zone containing a catalyst composed of asiliceous cracking component of high cracking activity intimatelyassociated with up to about 5% of a component selectively promotinghydrogenation reactions, said cracking zone being maintained at atemperature in the range of about 800-900 F., under a pressure of1500-3500 pounds per square inch, at least three mols of hydrogen beingcharged to said cracking zone per mol of total hydrocarbons includingrecycle, and said total hydrocarbons being fed to said cracking zone ata liquid space rate of 0.5 to 4 volumes of oil per hour per volume ofcatalyst; recovering from the vapor eflluent from said cracking zone agas rich in hydrogen and a bottoms fraction having an initial boilingpoint of 350-450 F., continuously and exhaustively recycling saidbottoms fraction and a portion of said hydrogen-rich gas to saidhydrogenative cracking zone, further separating from the vapor eluent afraction consisting essentially of normally gaseous hydrocarbons and aC4 fraction, separating the remaining hydrocarbons in said effluent intoat least two fractions including a comparatively high octane lightgasoline fraction having an end point in the range of 180-240" F. and apoor octane cracked naphtha fraction boiling in a range thereabove andcomprising naphthenic hydrocarbons, subjecting only said cracked naphthafraction to a reforming operation, involving selectively dehydrogenatingnaphthenes in said cracked naphtha fraction in a reforming zonecontaining a dehydrogenation catalyst having no significant crackingactivity, said zone being maintained at a temperature in the range of70D-950 F. and under a pressure of 500-1500 pounds per square inch, atleast 3 mols of hydrogen per mol of naphtha being charged to saidreforming zone and said naphtha being charged to said zone at the rateof at least 1 liquid volume per hour per volume of catalyst, whereby nosignificant coke deposits in said reforming zone, separating ahydrogen-rich gas from products formed in said reforming zone andreturning said gas to said cracking zone, and blending reformed gasolinefrom said reforming zone with the light gasoline fraction from saidcracking zone and suflicient C-4 hydrocarbons therefrom to adjust thethus upgraded gasoline to desired vapor pressure.

References Cited in the le of this patent UNITED STATES PATENTS1,919,857 Pier et al July 25, 1933 1,933,107 G h 1933 1,949,230 19342,285,727 1942 2,334,159 1943 2,358,879 1944 2,372,711 Cornforth Apr. 3,1945 2,451,041 Murphree Oct. 12, 1948 2,467,966 Clark Apr. 19, 19492,550,531 Ciapetta Apr. 24, 1951 2,596,145 Grote May 13, 1952 OTHERREFERENCES Weber: Oil and Gas Journal, vol. 49, No. 1, pages 66-69,86-88, May 11, 1950.

1. THE METHOD OF PRODUCING HIGH YIELDS OF GASOLINE OF GOOD OCTANEQUALITY WHICH COMPRISES REMOVING FROM PETROLEUM AT LEAST THOSE MATERIALSBOILING IN THE RANGE OF GASOLINE TO PROVIDE AN INITIAL HYDROCARBONCHARGE, HYDROGENATIVELY CRACKING SAID INITIAL HYDROCARBON CHARGE AT APRESSURE IN EXCESS OF ABOUT 750 POUNDS PER SQUARE INCH AND IN THEPRESENCE OF A CATALYST COMPOSED OF A MINOR QUANTITY OF A COMPONENTHAVING SELECTIVE HYDROGENATING ACTIVITY INTIMATELY ASSOCIATED WITH ACOMPONENT HAVING CRACKING ACTIVITY, REMOVING A HYDROGEN-RICH GAS STREAMFROM THE EFFLUENT, SEPARATING THE REMAINDER OF THE EFFLUENT INTOFRACTIONS COMPRISING AT LEAST: A C-4 FRACTION, A LIGHT GASOLINE FRACTIONOF COMPARATIVELY HIGH OCTANE VALUE COMPOSED OF HYDROCARBONS BOILINGABOVE THE C4 FRACTION AND BELOW 240* F., A CRACKED NAPHTHA FRACTIONINCLUDING NAPHTHENIC HYDROCARBONS BOILING IN THE UPPER PORTION OF THEGASOLINE RANGE, AND A RESIDUAL GAS OIL FRACTION BOILING IN A RANGE ABOVESAID LAST NAMED NAPHTHA FRACTION; CONTINUOUSLY AND EXHAUSTIVELYRECYCLING SAID RESIDUAL GAS OIL FRACTION TO SAID HYDROGENATIVE CRACKING,REFORMING ONLY SAID CRACKED NAPHTHA FRACTION SUBSTANTIALLY FREE FROMLOWER BOILING HYDROCARBONS UNDER DEHYDROGENATING CONDITIONS AND IN THEPRESENCE OF A DEHYDROGENATING CATALYST, SAID CONDITIONS AND CATALYSTBEING SELECTED TO DISFAVOR SUBSTANTIAL COKING AND CRACKING OF SAIDNAPHTHA FRACTION INCLUDING PRESSURE ABOVE 300 POUNDS PER SQUARE INCH,RECOVERING FROM PRODUCTS OF DEHYDROGENATION A HYDROGENRICH GAS AND AREFORMED GASOLINE FRACTION OF DESIRED END POINT, RETURNING AT LEAST APORTION OF SAID HYDROGEN-RICH GAS FROM DEHYDROGENATION TO SAIDHYDROGENATIVE CRACKING STEP, BLENDING SAID REFORMED GASOLINE FRACTIONWITH SAID LIGHT GASOLINE FRACTION DERIVED FROM HYDROGENATIVE CRACKINGAND ADDING TO THE BLEND A SUFFICIENT PORTION OF SAID C-4 FRACTION TOPRODUCE GASOLINE OF DESIRED VAPOR PRESSURE, AND RECYCLING TOHYDROGENATIVE CRACKING ANY HYDROCARBONS BOILING ABOVE THE DESIRED ENDPORTION OF THE REFORMED GASOLINE, WHEREBY ALL OF THE HYDROCARBONS INSAID INITIAL CHARGE ARE CONVERTED TO PRODUCTS BOILING NO HIGHER THANSAID DESIRED GASOLINE END POINT.